The monitoring of ventilation and its pattern has heretofore been difficult if not impossible in many situations where measurements are important. All previously employed means for accurately measuring ventilation have, for example, required the use of either a mouthpiece or a mask. Such masks or mouthpieces cannot always be used with critically ill patients. Further, these devices add dead space and resistance to the breathing which is being measured. Additionally, spirometers and flowmeters, which have frequently been heretofore used, limit the freedom of movement of individuals and their accuracy is adversly affected by changing environment.
In an attempt to overcome some of these difficulties, pairs of electromagnets and magnetometers have been placed on the surface of the rib cage and abdomen to measure linear dimension changes and estimate lung volume changes. However, single anterior-posterior pairs of magnetometers on the rib cage and abdomen, while fairly quantitative for quiet breathing become increasingly inaccurate as breath volume increases. This is also true during resistive breathing or forced expirations or when posture varies. As volume is increased from normal or during increased respiratory efforts, the rib cage and abdomen no longer behave with a single degree of freedom, so single magnetometer pairs cannot quantitatively measure these maneuvers. That is, there are changes in the cross-sectional dimensions of the chest wall in the lateral dimension which are not reflected in anterior-postierior movements.
It is, accordingly, an object of the present invention to provide an improved method and apparatus for the non-invasive, accurate measurement of ventillation, including pattern and fractionation.
It is a further object of the present invention to provide a system which dispenses with a mouthpiece or mask during measurement of ventilation and which can be used accurately in most environments and situations without constraining or requiring alteration of posture of the subject.
Still a further object of the present invention is to avoid a system which adds dead space and resistance to breathing while measurements are being made.